The exhaust from a coal-fired power plant is about 12 per cent carbon dioxide, while in steel and cement production it is typically double that.
Unlike CCS, which by itself only prevents additional carbon dioxide from entering the atmosphere, DAC extracts carbon dioxide molecules already there.
Crucially, this makes DAC a "negative emissions" technology.
It can therefore generate credits for companies seeking to offset their greenhouse gas output - but only if the captured carbon dioxide is permanently stored underground, such as in depleted oil and gas reservoirs or in saline aquifers.
The concentration of carbon dioxide in ambient air is only 420 parts per million (about 0.04 per cent), so corralling carbon dioxide using DAC is far more energy intensive.
Once isolated using either CCS or DAC, carbon dioxide can be used to make products such as building materials or "green" aviation fuel, though some of that carbon dioxide will seep back into the air.
"If the carbon dioxide is utilised, then it is not removal," said Oliver Geden, a senior fellow at the German Institute for International Security Affairs.
STATE OF PLAY
The fossil fuel industry has been using CCS since the 1970s but not to prevent carbon dioxide from leaching into the atmosphere.
Rather, oil and gas companies inject carbon dioxide into oil fields to extract more crude more quickly.
Historically, bolting CCS facilities onto coal- and gas-fired power plants and then storing the carbon dioxide to reduce emissions has proven technically feasible but uneconomical.
The world's largest CCS plant, the Petra Nova facility in Texas, was mothballed three years after opening in 2017.
But the looming climate crisis and government subsidies have revived interest in CCS for the power sector and beyond.
At the end of 2022, there were 35 commercial-scale facilities worldwide applying carbon capture technology to industry, fuel transformation or power generation, isolating a total of 45 million tonnes (Mt) of carbon dioxide, according to the International Energy Agency (IEA).
DAC, by contrast, is very new.
A total of 18 DAC plants globally only captured about as much carbon dioxide last year (10,000 tonnes) as the world emits in 10 seconds.
SCALING UP
Both CCS and DAC must be massively scaled up if they are to play a significant role in decarbonising the global economy.
To keep the mid-century net-zero target in play, CCS will need to divert 1.3 billion tonnes a year from power and industry - 30 times more than last year - by 2030, according to the IEA.
DAC must remove 60Mt carbon dioxide per year by that date, several thousand-fold more than today.
But the nascent industry is burgeoning with new actors, and the first million-tonne-per-year plant is scheduled to come on line in the United States next year, with others following.
"It's a huge challenge but it's not unprecedented," University of Wisconsin-Madison professor Gregory Nemet told AFP, citing other technologies, including solar panels, that have scaled up dramatically in a matter of decades.
Preparing a site to stock carbon dioxide can take up to 10 years, so storage could become a serious bottleneck for both CCS and DAC development.
COST PER TONNE
Carbon capture costs US$15 to US$20 per tonne for industrial processes with highly concentrated streams of carbon dioxide, and US$40 to US$120 per tonne for more diluted gas streams, such as in power generation.
